基于阵列盖革探测器的激光测距信号处理北大核心CSCD

传统激光测距中最常用的方法是采用工作在线性模式的单元APD进行光子探测,而随着探测距离增加,线性增益不满足使用需求,盖革模式APD应运而生。阵列探测盖革模式APD是具有探测单光子能级信号能力的新型探测器件,具有1×10^(6)至1×10^(7)的内增益,响应度高,但其受背景光影响较大,因此这一器件的信号处理难度极大。本文提出基于光子计数法的阵列信号处理的三种思路,均能够大幅提升信号对比度。其中多通道累加算法简单便捷、可实现性高;空间卷积池化算法具有高信号散布灵敏性;阵列拓展算法具备高信号辨识度。     

基于C/A码辅助的GPS M码信号盲解调

针对GPS M码信号受到C/A码和Y码信号的干扰难以直接进行解调的问题,提出了一种基于C/A码辅助的M码盲解调方法。利用解调后的C/A码信号校正信号频偏,通过I/Q支路分离实现将C/A码信号与Y码、M码信号的剥离,最后利用M码信号的特点进行相参增强进一步提高性能。实采数据的解调实验证明了所提算法的可行性。     

基于一种非等距线阵的宽带信号处理方法

获得宽带信号的波达方向,提出一种基于非等距的参差线阵方法。利用孙子定理、解模糊条件、分频带相控阵等方法解释非等距线阵。构造出的参差线阵通过处理合成,保持阵列对不同频率指向的一致性,达到信号功率非相参积累的预期效果。解模糊得到信号的波达方向,通过实验仿真验证方法可行。     

一种全球定位系统弱信号捕获策略

信号捕获是目前广泛应用的数字全球定位系统(GPS)接收机的重要部分,弱信号条件下的信号捕获过程是目前GPS接收机算法研究的重点。本文分析和比较了2种经典捕获检测策略(TONG捕获策略及NM捕获策略)的性能,并针对弱信号条件下GPS信号捕获的特点,提出了一种适用于弱信号条件下的捕获检测策略—双门限搜索检测策略。理论分析和仿真说明该策略在弱信号条件下具有较好的性能。     

基于MDBZP 的C/A码信号高灵敏捕获算法

卫星信号的捕获是GPS接收机信号处理的首要任务。针对在微弱信号的情况下传统捕获方法不能很好地捕获到卫星信号的问题,提出一种改进的二倍分组块补零（MDBZP）方法为高灵敏度GPS接收机提供理论依据。该方法将连续相干积分分解成普通循环相关和随后的傅里叶变换来产生不同的多普勒频移搜索,并针对连续积分跨越多个导航电文数据位的情况给出解决方案,同时考虑了多普勒效应对码长造成的影响。仿真结果表明,此方法对低至15dB-Hz的微弱信号C/A码信号仍有较好的捕获能力。最后给出了不同载噪比情况下所对应的检测信噪比。     

基于MDBZP 的C/A码信号高灵敏捕获算法

卫星信号的捕获是GPS接收机信号处理的首要任务。针对在微弱信号的情况下传统捕获方法不能很好地捕获到卫星信号的问题,提出一种改进的二倍分组块补零( MDBZP)方法为高灵敏度GPS接收机提供理论依据。该方法将连续相干积分分解成普通循环相关和随后的傅里叶变换来产生不同的多普勒频移搜索,并针对连续积分跨越多个导航电文数据位的情况给出解决方案,同时考虑了多普勒效应对码长造成的影响。仿真结果表明,此方法对低至15 dB-Hz的微弱信号C/A码信号仍有较好的捕获能力。最后给出了不同载噪比情况下所对应的检测信噪比。     

Perspective/navigation-The Global Positioning System

A brief history of navigation is given, highlighting the needs that led ultimately to the development of 3-D satellite based navigation. The evolution of Navstar, commonly known as GPS (Global Positioning System), is traced from its initial conception in 1960. The use of bandwidth compression to overcome the SNR problem is discussed. An explanation of how the GPS works is provided. Civilian as well as military applications are examined     

基于双单片机的线阵CCD驱动及信号处理系统

针对线阵CCD器件的驱动和信号处理,使用了2片STC11F02单片机,一片产生CCD驱动时序信号,另一片负责测量控制及与上位机进行通信。采用硬件的方法对CCD输出信号进行处理,直接得到光斑中心位置,不需要进行A/D转换。试验结果说明测量精度可达0.007 mm。该电路成本低,体积小,速度快,可广泛应用于基于线阵CCD的非接触式几何量测量。     

Bilinear signal synthesis in array processing

Multiple source signals impinging on an antenna array can be separated by time-frequency synthesis techniques. Averaging of the time-frequency distributions (TFDs) of the data across the array permits the spatial signatures of sources to play a fundamental role in improving the synthesis performance. Array averaging introduces a weighting function in the time-frequency domain that decreases the noise levels, reduces the interactions of the source signals, and mitigates the crossterms. This is achieved independent of the temporal characteristics of the source signals and without causing any smearing of the signal terms. The weighting function may take noninteger values, which are determined by the communication channel, the source positions, and their angular separations. Unlike the recently devised blind source separation methods using spatial TFDs, the proposed method does not require whitening or retrieval of the source directional matrix. The paper evaluates the proposed method in terms of performance and computations relative to the existing source separation techniques based on quadratic TFDs.     

基于多通道阵列处理的二次雷达混扰信号分选

针对应答脉冲信号的同步干扰(即混扰)造成二次雷达询问机解码错误的问题,提出了基于多通道阵列处理的混扰信号分选算法。首先建立了询问机天线使用多通道阵列的混扰信号模型,在此基础之上给出了应答机个数及其到达角估计算法,并提出了基于最大似然估计的应答信号分选算法。仿真结果表明,该算法能够从混扰信号中同时准确分离多个应答信号,性能明显优于FastICA算法。当信噪比高于10 dB时,所提算法的分离指数比FastICA算法至少低10 dB。     

Spoofing detection in IEEE 802.15.4 networks based on received signal strength

The shared medium used in wireless networks makes them vulnerable to spoofing attacks, in which an adversary masquerades as one or more legitimate nodes to disturb normal operation of the network. In this paper we present a novel spoofing detection method for static IEEE 802.15.4 networks based on spatial correlation property of received signal strength (RSS). While most existing RSS based techniques directly process RSS values of the received frames and rely on multiple traffic air monitors (AMs) to provide an acceptable detection performance, we extract features of RSS streams to reduce data redundancy and provide a more distinguishable representation of the data. Our algorithm employs two features of RSS streams, summation of detailed coefficients (SDCs) in discrete Haar wavelet transform (DHWT) of the RSS streams and the ratio of out-of-bound frames. We show that in a typical scenario, a single AM with SDC as detection parameter, can theoretically outperform a system with 12 AMs which directly applies RSS values as detection parameter. Using ratio of out-of-bound frames facilitates detection of high rate attacks. In addition, we suggest adaptive learning of legitimate RSS values which enhances the robustness of the attack detector against environmental changes. Using both magnitude and frequency related features, we achieved high detection performance with a single AM; this enables development of preventive measures for spoofing attacks. The performance of our approach was evaluated through an IEEE 802.15.4 testbed in an office environment. Experimental results along with theoretical analysis show that the proposed method outperforms the existing RSS-based spoofing detection solutions. Using a single AM, we were able to attain 94.75% detection rate (DR) with 0.56% false positive rate (FPR). For 4 AMs, the results improved to 99% DR and 0% FPR.     

基于平均相关和差分相干累积的微弱GPS C/A码信号精密捕获算法

针对弱信号条件下GPS C/A码捕获问题,提出一种基于平均相关和差分相干累积的码捕获算法。首先,引入相干能量最大值与第二大值的比值作为判决变量,仿真了各种捕获算法的虚警概率得到最佳的判决门限;然后,通过设置的判决门限获得不同多普勒频率偏差及信噪比条件下的检测概率;最后,比较了所提差分相干累积算法、相干非相干累积算法以及非相干累积算法的捕获灵敏度。仿真实验表明,在相同接收数据长度的情况下,采用差分相干累积算法比其他2种算法提高捕获灵敏度约2 dB。     

A robust adaptive array based on signal subspace approach

In this note, we propose a signal subspace approach that improves the performance of a beam steered adaptive array in the presence of steering errors due to look-direction error (LDE) and/or random steering error (RSE). In the method, the degrees of freedom (DOF) are reduced so as not to cancel the desired signal while preserving the optimal characteristic of the array, and thus the weights of the array are determined by a linear combination of the eigenvectors of the signal subspace. The proposed method works as far as the eigen decomposition of the input covariance matrix into signal and noise subspaces is possible. The proposed method improves noticeably the array performance of the beam steered array in the presence of steering errors and provides the optimum array performance in the absence of steering errors     

FFT与循环卷积相结合的GPS信号C/A码相位测量算法

提出了一种将FFT与循环卷积相结合的算法,可以快速高精度测量GPS信号的C/A码相位。算法的主要思想是在较低的采样频率下用FFT法对GPS信号C/A码相位进行粗测,然后用循环卷积法在更高的采样频率下根据粗测结果进行细测,从而以较低的计算量实现对GPS信号的C/A码相位高精度测量。该算法主要应用于辅助式卫星定位接收机的开发和高精度扩频测距等领域。     

基于TMS320C6205的多媒体信号采集处理系统

介绍了TMS320C6205 DSP的基本特点和功能，并详细介绍了如何采用TMS320C6205 DSP并结合其它器件来实现一个多媒体信号采集处理系统。     

GPS C/A码发生器的仿真研究与FPGA设计

全球定位系统（Global Positioning System,GPS）能够向全球范围内的用户提供全天候的高精度导航、定位和授时服务,在军用和民用领域得到了广泛的应用.以GPS系统的测距码粗码C/A码为研究对象,在深入研究C/A码信号生成原理的基础上,利用Matlab中的Simulink对C/A码信号的生成进行了建模、仿真和分析,并利用FPGA设计并实现了C/A码发生器,详细说明了C/A码生成的设计原理,对其中的关键模块进行了设计和分析,给出了具体实现方案,同时阐述整个应用程序的流程,设计采用抽头选择控制端设置产生不同GPS卫星号的C/A码,最终仿真进一步验证了其结果的正确性,它可以产生任意GPS卫星号的C/A码,设计中采用VHDL语言实现的C/A码程序,可应用于基于FPGA的GPS接收机设计中,对研究我国的北斗导航系统接收机有一定的借鉴意义.     

基于InGaAs单光子探测器的线阵扫描激光雷达及其光子信号处理技术研究

随着探测体系的发展,基于单光子探测技术的光子计数激光雷达受到了广泛关注,有效降低了系统对激光功率的需求,广泛应用在远距离测距及成像领域。针对激光雷达在人眼安全波段的工作需求,基于自由运转模式InGaAs/InP SPAD单光子探测器设计了一套多元收发的远程线阵光子计数激光雷达扫描成像原型系统,对探测器在日光背景下的探测概率影响因素展开了分析,配合主动淬灭电路设计及工作温度、偏压调整获得了系统的最佳工作点,并针对扫描视场中孤立目标特征采用了点云滤波及后脉冲预处理算法,将单个接收通道的原始数据率由200 kbps量级降低至小于1 kbps。与记录单次回波相比,单个测距周期记录四次回波可将有效数据量提升约5%。同时也对探测器的噪声及后脉冲等特性进行了分析。该系统工作波段为1 550 nm,探测器线阵规模可达到128元,激光重频为20 kHz,可在2 s内实现水平200°范围内的激光三维成像,作用距离>3 km。经过成像算法处理,该系统在日光条件下成功实现多距离目标三维成像,成像目标清晰。     

采用压缩感知的标准测控信号处理

针对测控通信信号接收端存在数据大量冗余的问题,利用标准测控信号在频域上的稀疏性,采用压缩感知的理论进行前期处理。分别考虑了只存在测距音、只存在遥测信号和两类信号都存在等三种条件下的信号处理问题。通过改变稀疏度的大小,可以在不影响解调性能的条件下,大幅度降低接收端所需要的采样率,并且达到消除系统中不需要的谐波的目的。仿真验证了方法的有效性,同时说明利用压缩感知技术,将为测控通信系统的射频直接采样和处理提供一种高效的方式。     

Maximum likelihood estimation and MUSIC in array localization signal processing: A review

Algorithms to treat the maximum likelihood (ML) estimation problem in array localization signal processing are reviewed, including the alternating projection method, the iterative quadratic maximum likelihood method and the expectation-maximization method. The relationship of ML estimators and the MUSIC algorithm is presented. The Cramer-Rao bounds for the deterministic and stochastic models in array localization are summarized. Finally, the problem of the estimation of the number of sources is discussed.     

一种新型基于Strobe相关的BOC信号多径抑制算法

多径干扰信号是导航接收机测量过程中遇到的主要误差源之一。针对Galileo系统以及GPS现代化过程中拟使用的BOC调制信号,研究了基于Strobe相关的BOC信号跟踪过程中的多径抑制方法。分析了多径效应对码跟踪精度的影响,从鉴相函数入手,提出了一种新的En-Strobe相关法。运用窄相关法、Strobe相关法和En-Strobe相关法对BOC(1,1)信号和CBOC(6,1,1/11)信号进行多径抑制性能分析。仿真结果表明En-Strobe相关法在中短延迟的情况下能够很好的抑制多径误差,且性能优于窄相关法和Strobe相关法。